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 Post subject: propane butane ratio
PostPosted: Sun Jun 02, 2013 1:25 am 
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Joined: Fri Sep 03, 2010 9:47 am
Posts: 32
The percentage of butane varies depending on now much the gas companies want to dump that week.
Is there anywhere you can get pure propane? The only source I can see is "barbeque gas", which
would mean rigging up an adapter to fill your autogas tank from the bottle.
Or fitting the gas bottles in your vehicle (which would surely upset the insurance company).


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 Post subject: Re: propane butane ratio
PostPosted: Sun Jun 02, 2013 8:35 am 
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Joined: Wed Apr 09, 2008 9:00 am
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Location: Peterborough
I assume you are in Oz or NZ as you are posting in that section but can only tell you how it works in the UK. You can buy pure Propane from a gas supplier but, as you say, it comes in bottles. You can use and adapter and a pump to transfer from bottles to your car but you would need to invert the bottle as the take off is for vapour and not liquid. It won't be particularly quick and, as the bottles have been refilled many times, you can end up with quite a lot of heavy ends going into your tank too.

But why do you need pure Propane? Autogas sold in the UK is supposedly 100% Propane although it probably does contain a small proportion of Butane. In Europe, Autogas is often a mix of Propane and Butane at anything from a 90/10 to 50/50 ratio. Butane is denser than Propane so you get more weight per litre and as the stoichiometric ratio is by weight then you will get better economy running a mixture than you will on pure Propane. The stoichiometric ratio for perfect combustion is slightly higher too so you will actually use less of it. The only downsides are that it has a much higher boiling point, around 0 degrees C, so won't vaporise at low temperatures and has a lower Octane rating. So unless you are in sub-zero temperatures, doubtful in Oz, or you have tuned your engine to take advantage of the 113 RON Octane rating of Propane, you will gain nothing by running pure Propane over a Propane/Butane mix.

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 Post subject: Re: propane butane ratio
PostPosted: Sat Jun 22, 2013 11:51 am 
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Joined: Fri Jun 22, 2007 10:12 am
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You can buy straight propane from Supagas, usually cheaper than the servos too.

IIRC LPG is a 80/20 mixture here.


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